Phonograph pikcup cartridge



1952 J. F. WOOD 3,057,971

PHONOGRAPH PICKUP CARTRIDGE Filed Oct. 17, 1957 NETAZ CONT/967' BAADES PUBBEE CONT/1c 7'5 United States Patent 3,057,971 PHONOGRAPH PICKUP CARTRIDGE John F. Wood, Buchanan, Mich assignor to' Electro- Voice, Incorporated, Buchanan, Mich., a corporation of Indiana Filed Oct. 17, 1957, Ser. No. 690,724 8 Claims. (Cl. 179-100.41)

The present invention relates to a phonograph pickup cartridge, and more particularly to an improvement in certain characteristics of the type of cartridge disclosed in United States Letters Patent 2,793,254 for a Cartridge Case and Turnover Mechanism by John F. Wood, granted May 21, 1957, and United States Letters Patent 2,852,619 entitled Phonograph Cartridge, by John F. Wood, these applications having been assigned to the assignee of the present application.

In United States Patent 2,793,254 and United States Patent 2,852,619, there is disclosed an improved cartridge case containing a piezoelectric element supported in a pivoted or hinged manner by a pair of sheet metal contact members arranged transversely to the axis of the casing. While that structure has been found to be highly satisfactory, it has been indicated that it might be desirable to make certain improvements therein, particularly to obtain a better low frequency response. Accordingly in accordance with the present invention an improved reliability of electrical contact with the piezoelectric element was accomplished together with improved damping resulting in lower needle talk and reduced coupling to the tone arm by a changed support arrangement for the hinged or pivoted end of the piezoelectric element, thus providing increased compliance. I

It, therefore, is an object of the present invention to provide an improved phonograph cartridge having greater compliance.

Another object of the present invention is to provide aphonograph cartridge having improved damping and lower resonant frequency characteristics.

Another object of the invention is to provide a phonograph cartridge having greater uniformity in manufacture and improved reliability of electrical contact with the piezoelectric element.

Still another object of the invention is to provide a phonograph cartridge having lower needle talk and reduced coupling to the tone arm.

Still another object of the invention is to provide an improved electrically conductive contact and damping material for use in phonograph pickup cartridges.

These and other objects of the invention subsequently will become apparent by reference to the following description taken in conjunction with the accompanying drawing, wherein:

FIGURE 1 is an axial cross-section of a phonograph cartridge embodying the present invention;

FIGURE 2 is an end view of a portion of the cartridge support mechanism of FIGURE 1;

FIGURE 3 is an enlarged view of a portion of the cross-sectional view of FIGURE 1; and

FIGURE 4 is a curve showing the improved low frequency response characteristic.

Referring to FIGURES 1, 2 and 3 it will be noted that a cartridge support and turnover mechanism 11 is provided with peripherally arranged teeth 12 and a stop member 13 located within a support sleeve 14. The teeth 12 are engaged by a tooth gear 15 forming a part of the cartridge turnover mechanism. The cartridge turnover mechanism and support member 11 at one end is provided with a protuberance 16 which separates two electrical contact members 17 and 18, to which wires are connected leading through the tone arm.

The phonograph pickup cartridge 19 comprises a gen- Patented Oct. 9, 1962 erally tubular housing 20 having an axial bore 21 of a larger diameter than an adjacent axial bore 22 thereby forming a shoulder at an intermediate point between the two ends of the cartridge casing 20. At the shoulder formed by the two bores 21 and 22 there is provided an intermediate resilient support member 23 having a piezo electric element 24. The piezoelectric element 24 at its free end is provided with a rigid member 25 carrying a plurality of styli 26 for engaging the grooves of a phonograph record. The bore 22 leads to a reduced diameter bore 23 which is intersected by two transversely arranged openings 27 which extend through the cartridge casing 20. Each of the openings 27 preferably is in the form of a parallelogram, however, they may be in round or elliptical form if greater compliance is desired. The casing 20 is provided with a projecting fin or ridge member 28 which fits into a slot in the support member 11 to properly orient the cartridge 20 with respect to the turnover mechanism.

Two similar conductive rubber members 29, which conform to the surfaces of the openings 27, here in the form of parallelepipedons, are mounted in the trapezoidal openings 27. The rubber members 29 engage opposite surfaces of the piezoelectric element 24 to make electrical contact therewith. The conductive members 29 extend a short distance to the exterior of the housing 20 for engagement with the electrical contacts 17 and 18 within the support member 11. It will be noted from FIGURE 3 that the member 18 terminates in a curved portion so" as to engage the protruding conductive rubber member 29 and deforming this provides an electrical contact over an extended surface of the contact 18. Thus, the areas for electrical contact with the piezoelectric element 24' and with the contact elements 17 and 18 are appreciably greater than could be obtained by the use of metallic members.

The conductive members 29 are made of a composition which might be calledconductive rubber, the formula for which will subsequently be given. The conductive rubber members 29 still provide a pivoted type of support for the inner end of the piezoelectric element 24 in accordance with the teachings of the aforementioned Patent 2,793,254. The resiliency of the conductive members 29 provides an increased compliance of the cartridge element, improved damping resulting in lower needle talk and reduced coupling to the tone arm, and an improved lower resonant frequency characteristic.

In FIGURE 4 there is shown in curve A the frequency response curve of a cartridge constructed in accordance with the aforementioned patent. The curve B shows the improved frequency response characteristic of the same cartridge with rubber members 29 substituted for metal contact blades. The improvement is a result of the cartridge having a lower mechanical resonant frequency and a less sharp resonance. Thus, it will be seen that the lower frequency response has been greatly improved.

The resultant resonant frequency of the combination employing the rubber or foraminous contact is somewhat lower than as if metal contacts were employed. This is due to the improved compliance of the rubber contacts, since arm resonance depends upon cartridge compliance, Cm, and arm mass, M, according to 211/ M C m The reduced resonance sharpness and increased compliance of the cartridge minimize mis-trackin-g and distortion at the low frequencies and enable lower frequencies to be reproduced.

The conductive rubber of electrically conductive foraminous composition employed for the contacts 29 is as follows:

Parts Natural rubber (crepe) 100 Reogen; a mixture of oil soluble sulphonic acid with paraffin oil Zinc oxide 4 Stearic acid 1 Paraflin 2 Lamp black 100 Tetramethylthiuram-disulfide 3 Mercapto-benzothiazole .5 Altax (benzothiazol disulfide) 1 'While for the purpose of illustrating and describing the present invention certain embodiments and a preferred composition have been shown and described, it is to be understood that the invention is not to be limited thereby but such equivalents are contemplated as may be commensurate with the spirit and scope of the appended claims.

I claim as my invention:

'1. A phonograph pickup cartridge comprising an elongated casing having an axial cavity extending therein from one open end to a closed end, two, pair of apertures adjacent to said closed end, the apertufes of each pair being on one of two planes parallel to each other and traversing the cavity of the casing parallel to the axis of elongation thereof, an elongated piezoelectric element mounted between the two parallel planes, and an electrically conductive rubber contact member mounted in each pair of apertures, each contact member extending between and through the apertures of one pair and engaging one of the flat sides of said piezoelectric element adjacent the inner end thereof, said contact members each extending beyond the exterior of said casing.

2. A phonograph cartridge according to claim 1 wherein said conductive contact members have parallelogram cross-sections.

3. The phonograph cartridge according to claim 2 wherein said plurality of transverse apertures have parallelogram cross-sections.

4. The phonograph cartridge according to claim 2 wherein said piezoelectric element at its free end has affixed thereto a rigid member carrying a phonograph stylus.

5. An electrically conductive foraminous composition comprising 100 parts natural rubber, 10 parts oil soluble sulphonic acid mixed with paraffin oil, 4 parts zinc oxide,

1 part stearic acid, 2 parts parafiin, 100 parts lamp black, 3 parts tetramethylthiuram-disulfide, 0.5 part mercaptobenzothiazole, and 1 part benzothiazol disulfide.

6. A phonograph pickup cartridge comprising the elements of claim 1 wherein the electrically conductive rubber contact members comprise 100 parts natural rubber, 10 parts oil soluble sulphonic acid mixed with parafiin oil, 4 parts zinc oxide, 1 part stearic acid, 2 parts paraflin, 100 parts lamp black, 3 parts tetramethylthiuram-disulfide, 0.5 part mercapto-benzothiazole, and 1 part 'benzothiazol disulfide.

7. A phonograph pickup comprising a casing, an elongated piezoelectric element disposed within the casing, and a pair of electrically conductive rubber contact members mounted on the casing and disposed between the casing and opposite sides of the piezoelectric element, said contact members mounting the piezoelectric element on the casing.

8. A phonograph pickup comprising the elements of claim 7 wherein the casing is elongated and includes an axial cavity extending into the casing from an open end and two pairs of apertures intersecting the cavity remote from opening, each of the conductive rubber contact members being disposed in one of the pairs of apertures and extending across the cavity, said contact members extending through the apertures to the exterior of the casing.

References Cited in the file of this patent UNITED STATES PATENTS 1,557,931 Otto Mar. 23, 1926 2,240,855 Phillips May 6, 1941 2,284,579 Jones May 26, 1942 2,429,137 Root Oct. 14, 1947 2,471,601 Albright May 31, 1949 2,545,737 Luke Mar. 20, 1951 2,568,673 Washbum Sept, 18, 1951 2,703,343 Snepvangers Mar. 1, 1955 OTHER REFERENCES Habgood et al.: Rubber Chem. & Tech., vol. 15, pp. 146157.

Stern: Rubber: Natural and Synthetic, pp. 107.

Chemistry of Natural and Synthetic Rubbers, July 1, 1957, pp. -47. 

